The present invention relates generally to thin film deposition and etching systems. In particular, the present invention relates to methods and apparatus for depositing thin films with very high uniformity. The present invention also relates to methods and apparatus for etching material at highly uniform etch rates.
There are three common techniques used to deposit thin films onto substrates. These techniques are evaporation, ion beam deposition, and magnetron sputtering. FIG. 1 illustrates a schematic diagram of a prior art electron beam evaporation deposition system 10. The evaporation system 10 is enclosed in a vacuum chamber 12. An electron gun 14 generates an electron beam 16 that is used to heat a crucible 18 containing the deposition material to a temperature that causes the deposition material to evaporate. The electron beam is deflected with a magnet 20 that causes the electron beam to strike the desired location in the crucible 18. Typical evaporation systems have multiple crucibles.
Some Evaporation systems include multiple sources and multiple electron guns that produce deposition material from two or more sources and deposit the deposition material simultaneously onto a substrate. Alternatively, a thermal heating element (not shown) is used to heat the crucible 18. A substrate support 22 that typically supports multiple substrates 23 is positioned in the path of the evaporated material. In some known evaporation systems, the substrate support 22 is rotated with a motor 24 in order to increase the uniformity of the deposited thin film.
FIG. 2 illustrates a schematic diagram of a prior art ion beam sputter deposition system 50. The ion beam sputter deposition system 50 is enclosed in a vacuum chamber 52. An ion source 54 generates an ion beam 56 that is directed to one or more targets 58. The ion beam 56 strikes the target 58 and sputters neutral atoms from the target 58 with a stutter flux 60. A substrate support 62 that typically supports multiple substrates 64 is positioned in the path of the sputter flux 60. The sputter flux 60 bombards the substrates, thereby depositing a sputtered thin film. In order to increase the uniformity of the sputtered thin film, the substrate support 62 may be rotated with a motor 66. Ion beam sputtering is advantageous because it permits independent control over the energy and current density of the bombarding ions.
FIG. 3 illustrates a schematic diagram of a prior art magnetron sputter deposition system 80. The magnetron sputter deposition system 80 is enclosed in a vacuum chamber 82. The magnetron sputter deposition system 80 includes a diode device having an anode 84 and a cathode 86. A magnet 88 is positioned behind the cathode 86. Two ring-shaped cathodes and a disk-shaped anode are shown, but there are several other known configurations.
The cathode 86 is biased to a negative potential that is high enough to induce a breakdown in the surrounding gas and to sustain a plasma 90. The magnet 88 generates a magnetic field 92 behind the cathode 86 that traps electrons generated by the cathode 86. The electrons lose energy in spiral paths in the plasma 90 and are collected by the anode 84. The electrons enhance the bombarding efficiency of ions 94 in the plasma 90. Neutral atoms 96 are sputtered fit the cathode 86 with a sputter flux 98. The sputter flux 98 bombards the substrates 64, thereby depositing a sputtered thin film onto the substrate 64.
The substrates 64 in known systems are typically placed at a distance from the cathode 86 ranging between two and ten inches. In order to increase the uniformity of the sputtered film, the substrate support 62 may be rotated with a motor 66. Magnetron sputtering is advantageous because it has relatively high deposition rates, large deposition areas, and low substrate heating.
The deposition thickness uniformity achieved with these known techniques is limited by the flux uniformity achieved at the substrate plane and the type of substrate rotation. The flux uniformity can be adversely affected by target or deposition material imperfections that cause hot and cold spots, which affect the deposition rate. Typically, the flux uniformity changes with time. The flux uniformity can be improved somewhat by using a large target and/or by using a long distance from the target to the substrate. However, there are practical limits to the size of the target and the distance from the target to the substrate. Some applications, such as optical filters for high-speed optical communication systems, require thin film uniformities that cannot be achieved with these prior art techniques.
The present invention relates to methods and apparatus for depositing thin films using a differentially-pumped deposition source and deposition chamber, where the pressure in the deposition source is substantially higher than the pressure in the deposition chamber. The present invention also relates to methods and apparatus for using an ion source that generates an ion beam for ion beam assisted processing of the deposited thin films. In one embodiment, the ion beam and the deposition flux do not overlap and the ion beam is used for out-of-phase ion-beam-assisted processing. Both the deposition source and the ion beam source can be positioned a relatively short distance from the substrate, thereby exposing the substrate to a relatively high density of sputter flux and ion beam flux.
One embodiment of the deposition system of the present invention is a differentially-pumped magnetron sputtering system. The magnetron sputtering system has numerous advantages over known deposition systems. For example, the magnetron sputtering system deposits high purity, high-density films at high deposition rates with a high degree of uniformity and run-to-run consistency. In addition, the magnetron sputtering system has a long target lifetime and is relatively easy to maintain. Thin film uniformity can be improved by aperturing sputter flux from the sputter deposition source and then moving the substrates relative to the sputter flux with a dual-scan motion, such as a two dimensional motion. Thin film uniformity can also be improved by scanning one motion much faster than the other motion. Also, thin film uniformity can be improved by over-scanning.
Accordingly, the present invention features a differentially pumped deposition system that includes a deposition source that is positioned in a first chamber. In one embodiment, the deposition source is a magnetron sputter source. In another embodiment, the deposition source is an evaporation source. The deposition source generates deposition flux comprising neutral atoms and molecules.
A shield defines an aperture that is positioned in a path of the deposition flux. The shield passes the deposition flux through the aperture and substantially blocks the deposition flux from propagating past the shield everywhere else. The aperture may be shaped to increase the transmitted deposition flux. The aperture may also be shaped to reduce the over-scan area. A substrate support is positioned in a second chamber adjacent to the shield. The pressure in the second chamber is lower than the pressure in the first chamber.
The deposition system also includes a dual-scanning system that scans the substrate support relative to the aperture with a first and a second motion. The dual-scanning system may be a mechanical scanning system. The scan rate of the first motion. maybe substantially greater than the scan rate of the second motion The scan rate of at least one of the first motion and the second motion may also vary with time during deposition. In one embodiment the dual-scanning system comprises a rotational scanning system and a translational scanning system, wherein the first motion comprises a rotational motion having a rotation rate and the second motion comprises a translational motion having a translation rate. The rotation rate of the rotational motion may be at least five times greater than the translation rate of the translational motion.
The deposition system may include an ion source that generates an ion beam. The ion source is positioned in the second chamber so that the ion beam strikes the deposition area. The ion source may be positioned so that the ion beam does not overlap with the deposition flux. In addition, the deposition system may include an in-situ monitoring system that monitors properties of the thin film during deposition.
The present invention also features a method of depositing a uniform thin film that includes generating deposition flux at a first pressure. A substrate at a second pressure, which is lower than the first pressure, is exposed to the deposition flux. The deposition flux may be generated by magnetron sputtering. In one embodiment, the deposition flux is passed through an aperture. In one embodiment, the substrate is exposed to an ion beam. The ion beam may overlap with the deposition flux and may be used for in-phase ion beam processing. Also, the ion beam may not overlap with the deposition flux and may be used for out-of phase ion beam processing.
The substrate is scanned relative to the deposition flux with a first and a second motion. The dual-scanning motion improves the uniformity of the thin film. The scan rate of the first motion is greater than the scan rate of the second motion. In one embodiment, the first motion is a rotational motion having a rotational scan rate and the second motion is a translational motion having a translational scan rate. The rotational rate of the rotational motion may be at least five times greater than the translational scan rate. In one embodiment, the substrate is over-scanned relative to the deposition flux in at least one of the firs motion and the second motion.
The present invention also features an ion beam assisted deposition system that includes a deposition source that is positioned in a first chamber. A deposition source generates deposition flux comprising neutral atoms and molecules. The deposition source may be a magnetron sputter source. The ion source is positioned so that the ion beam does not overlap with the deposition flux.
A substrate support is positioned in a second chamber. The pressure in the second chamber is lower than the pressure in the first chamber. An ion source is positioned in the second chamber so that the ion beam strikes a deposition area on the substrate support. The ion source generates an ion beam that is used for ion beam assisted processing.
A dual-scanning system scans the substrate support relative to the aperture with a first and a second motion. The scan rate of the first motion is substantially greater than the scan rate of the second motion. The scan rate of at least one of the first motion and the second motion may vary with time during deposition. The dual-scanning system includes a rotational scanning system that scans the substrate support at a rotation rate and a translational scanning system that scans the substrate support relative to the aperture at a translational rate. The rotation rate of the rotational motion may be at least five times greater than the translation rate of the translational motion.
In one embodiment, the deposition system includes a shield that defines an aperture that is positioned in the pat of the deposition flux. The shield passes the deposition flux through the aperture and substantially blocks the deposition flux from propagating past the shield everywhere else. The aperture may be shaped to increase the transmitted deposition flux. The aperture may also be shaped to reduce the over-scan area. In one embodiment, the dual-scanning system includes an in-situ monitoring system that monitors properties of the thin film during deposition.
The present invention also features a method of out-of-phase ion beam assisted deposition. The method includes generating deposition flux at a first pressure. The deposition flux may be generated by magnetron sputtering. The deposition flux is deposited onto a substrate at a second pressure. The second pressure is lower than the first pressure. The substrate is exposed to an ion beam that does not overlap with the deposition flux.
In one embodiment, the substrate is scanned relative to the deposition flux with a first motion and a second motion. The dual-scan motion deposits a uniform thin film onto the substrate. In one embodiment, the first motion is a rotational motion having a rotational scan rate and the second motion is a translational motion having a translational scan rate. The scan rate of the first motion may be greater than the scan rate of the second motion. The rotational rate of the rotational motion may be at least five times greater than the translational scan rate.
In one embodiment, the deposition flux is passed through an aperture. In one embodiment, the substrate is over-scanned relative to the deposition flux in at least one of the first motion and the second motion.